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32 * This source files provides two important functions for dynamic
35 * - a C runtime initializer (__libc_preinit), which is called by
36 * the dynamic linker when libc.so is loaded. This happens before
37 * any other initializer (e.g. static C++ constructors in other
38 * shared libraries the program depends on).
40 * - a program launch function (__libc_init), which is called after
41 * all dynamic linking has been performed. Technically, it is called
42 * from arch-$ARCH/bionic/crtbegin_dynamic.S which is itself called
43 * by the dynamic linker after all libraries have been loaded and
52 #include "libc_init_common.h"
54 #include "private/bionic_globals.h"
55 #include "private/bionic_ssp.h"
56 #include "private/bionic_tls.h"
57 #include "private/KernelArgumentBlock.h"
60 extern void netdClientInit(void);
61 extern int __cxa_atexit(void (*)(void *), void *, void *);
64 // We flag the __libc_preinit function as a constructor to ensure
65 // that its address is listed in libc.so's .init_array section.
66 // This ensures that the function is called by the dynamic linker
67 // as soon as the shared library is loaded.
68 __attribute__((constructor)) static void __libc_preinit() {
69 // Read the kernel argument block pointer from TLS.
70 void** tls = __get_tls();
71 KernelArgumentBlock** args_slot = &reinterpret_cast<KernelArgumentBlock**>(tls)[TLS_SLOT_BIONIC_PREINIT];
72 KernelArgumentBlock* args = *args_slot;
74 // Clear the slot so no other initializer sees its value.
75 // __libc_init_common() will change the TLS area so the old one won't be accessible anyway.
78 // The linker has initialized its copy of the global stack_chk_guard, and filled in the main
79 // thread's TLS slot with that value. Initialize the local global stack guard with its value.
80 __stack_chk_guard = reinterpret_cast<uintptr_t>(tls[TLS_SLOT_STACK_GUARD]);
82 __libc_init_globals(*args);
83 __libc_init_common(*args);
85 // Hooks for various libraries to let them know that we're starting up.
86 __libc_globals.mutate(__libc_init_malloc);
90 // This function is called from the executable's _start entry point
91 // (see arch-$ARCH/bionic/crtbegin_dynamic.S), which is itself
92 // called by the dynamic linker after it has loaded all shared
93 // libraries the executable depends on.
95 // Note that the dynamic linker has also run all constructors in the
96 // executable at this point.
97 __noreturn void __libc_init(void* raw_args,
98 void (*onexit)(void) __unused,
99 int (*slingshot)(int, char**, char**),
100 structors_array_t const * const structors) {
102 KernelArgumentBlock args(raw_args);
104 // Several Linux ABIs don't pass the onexit pointer, and the ones that
105 // do never use it. Therefore, we ignore it.
107 // The executable may have its own destructors listed in its .fini_array
108 // so we need to ensure that these are called when the program exits
110 if (structors->fini_array) {
111 __cxa_atexit(__libc_fini,structors->fini_array,NULL);
114 exit(slingshot(args.argc, args.argv, args.envp));
117 extern "C" uint32_t android_get_application_target_sdk_version();
119 uint32_t bionic_get_application_target_sdk_version() {
120 return android_get_application_target_sdk_version();